Circulating material for hydrogen production and thermochemical hydrogen production method

Abstract

The present application provides a neutral circulating material capable of desorbing oxygen at 1000°C or lower, and a thermochemical decomposition hydrogen production method using the neutral circulating material. One embodiment of the present application relates to a circulating material for thermochemical hydrogen production, comprising a perovskite oxide represented by the general formula Ca x (RE) 1‑x MO 3‑δ (In the formula, RE is one or more selected from the group consisting of rare earth metals, M is one or more selected from the group consisting of cobalt, manganese, and iron, x is a real number in a range of more than 0 and 1 or lower, and δ is a real number in a range of 0 or more and less than 1, wherein when M consists only of iron, x is not equal to 1.)

Description

Technical Field

[0001] One aspect of the present invention relates to a circulating material for hydrogen production and a method for producing hydrogen using the circulating material, and more specifically, to a circulating material for producing hydrogen using a thermochemical cycle and a method for producing hydrogen using the circulating material. Background Technology

[0002] Hydrogen has garnered attention as a secondary energy source for clean energy systems that can replace fossil fuels. If hydrogen can be produced from an inexhaustible supply of water, the water source will not be depleted. Furthermore, water is produced during the combustion of hydrogen. Therefore, energy systems utilizing hydrogen will not emit CO2, which has environmental impacts.

[0003] To establish a hydrogen energy system, it is necessary to utilize primary energy sources that do not rely on fossil fuels, such as water, to produce hydrogen in large quantities and at low cost. Methods for producing hydrogen from water include electrolysis, photocatalysis, and thermochemical decomposition. Currently, water electrolysis is the most reliable method, but its power generation efficiency is limited by the efficiency of hydrogen production. Furthermore, in photocatalysis, since hydrogen and oxygen are produced simultaneously as decomposition products of water, it is necessary to prevent their recombination and to separate them using costly processes such as membrane separation.

[0004] On the other hand, the direct thermal decomposition of water requires the same free energy change (Δ) as the decomposition reaction (H2O→H2+1 / 2O2). r The temperature of water decomposition (G°) is above -4000°C. This water decomposition temperature can be lowered by dividing the reaction medium, known as the circulating medium, into multiple reactions (oxygen generation and water decomposition), resulting in hydrogen production with heat below 2000°C. In this thermochemical decomposition method, since electricity is not involved, power generation efficiency is not a concern, and membrane separation processes for hydrogen and oxygen are not required due to the division of the reactions. As a heat source and a primary energy source that does not rely on fossil fuels, the utilization of unused industrial waste heat such as solar thermal, high-temperature nuclear thermal, and steelmaking waste heat is envisioned, but the practical application and widespread adoption of a process capable of producing hydrogen have not yet been realized.

[0005] When using solar heat as a heat source, methods for securing heat by employing concentrating / thermal devices such as tower-type and dish-type structures have been investigated. For example, Non-Patent Literature 1 describes a concentrator with a high concentration ratio capable of obtaining heat exceeding 900°C.

[0006] Furthermore, Non-Patent Document 2 records the following: When using high-temperature nuclear heat as a heat source, a high-temperature gas furnace is being researched as a next-generation high-efficiency furnace, which is expected to be able to extract heat at 950°C.

[0007] Furthermore, when using unused industrial heat as a heat source, heat above 500°C can be extracted from the waste heat of steelmaking, which can obtain relatively high temperatures.

[0008] Therefore, if this heat can be effectively utilized as a heat source, hydrogen can be produced from primary energy sources that do not rely on fossil fuels. Research is underway on cyclic materials that can function below 1000°C and methods for producing hydrogen through thermochemical decomposition using these materials.

[0009] As a thermochemical hydrogen production process, the IS process and the UT-3 cycle are under research. Both processes cycle below 1000°C, but both involve reactions with strongly acidic circulating substances. Therefore, equipment used in this process is limited to reactors with high corrosion resistance, heat resistance, airtightness, and strength, and the high maintenance costs are a major obstacle to practical application and widespread adoption.

[0010] On the other hand, as a thermochemical hydrolysis process that does not involve strongly acidic cycling substances, a cycle based on the reduction reaction of metal oxides such as iron oxide and cerium oxide is being studied. Non-patent literature 3 describes high-temperature endothermic reactions (spontaneous oxygen desorption reactions) requiring 2200°C and 1600°C, respectively.

[0011] Furthermore, Patent Document 1 describes a catalyst for producing thermochemical fuels, characterized by producing fuel from thermal energy using a thermochemical cycle with two stages: a first temperature and a second temperature below the first temperature, and comprising a catalyst having the compositional formula AXO. 3±δ (where 0≤δ<1) It is composed of perovskite oxides (where A is any one or more of rare earth elements, alkaline earth metal elements or alkali metal elements, X is any one or more of transition metal elements or metalloid elements, and O is oxygen.).

[0012] Patent Document 1: International Publication No. 2013 / 141385

[0013] Non-patent literature 1: Lee A. Weinstein et al., Chem. Rev., 2015, 115, 12797-12838

[0014] Non-patent literature 2: Mineo et al., Journal of the Atomic Society of Japan, 2020, Vol. 62, No. 9

[0015] Non-patent literature 3: Xiaofei et al., INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 2022, 47, 33619-33642 Summary of the Invention

[0016] However, in the high-temperature endothermic reaction described above, a highly heat-resistant reactor is required, which limits the applicable heat sources.

[0017] Therefore, one objective of the present invention is to provide a neutral circulating substance capable of deoxygenation below 1000°C, and a method for producing hydrogen by thermochemical decomposition using the neutral circulating substance.

[0018] The inventors, through various studies on solutions to the aforementioned problems, discovered that in thermochemical hydrogen production methods, the use of materials of the general formula Ca as a recycling substance... x (RE) 1-x MO 3-δ (In the formula, RE is one or more selected from the group consisting of rare earth metals, M is one or more selected from the group consisting of cobalt, manganese and iron, x is a real number in the range of more than 0 and less than 1, and δ is a real number in the range of more than 0 and less than 1. Wherein, when M is composed only of iron, x is not equal to 1.) When a perovskite-type oxide is represented, it can be used to produce hydrogen by thermochemical water decomposition at temperatures below 1000°C, thus completing one aspect of the present invention.

[0019] That is, the essence of one aspect of the present invention is as follows.

[0020] (1) A circulating substance for thermochemical hydrogen production, comprising Ca x (RE) 1-x MO 3-δ (In the formula, RE is one or more selected from the group consisting of rare earth metals, M is one or more selected from the group consisting of cobalt, manganese and iron, x is a real number in the range of more than 0 and less than 1, and δ is a real number in the range of more than 0 and less than 1. When M consists only of iron, x is not equal to 1.) represents perovskite-type oxides.

[0021] (2) A thermochemical hydrogen production circulating substance comprising Ca x (RE) 1-x MO 3-δ (In the formula, RE is one or more selected from the group consisting of rare earth metals, M is one or more selected from the group including cobalt and manganese, x is a real number in the range of more than 0 and less than 1, and δ is a real number in the range of more than 0 and less than 1.) represents perovskite-type oxides.

[0022] (3) A thermochemical hydrogen production circulating substance comprising Ca x (RE) 1-x MO 3-δ (In the formula, RE is one or more selected from the group composed of rare earth metals, M is iron, x is a real number in the range of greater than 0 and less than 1, and δ is a real number in the range of greater than 0 and less than 1.) represents perovskite-type oxides.

[0023] (4) The circulating material for thermochemical hydrogen production according to any one of (1) to (3), further comprising a catalytic metal.

[0024] (5) Use of any one of (1) to (4) in thermochemical hydrogen production.

[0025] (6) A thermochemical hydrogen production method comprising the following steps: heating water and the thermochemical hydrogen production circulating material to be reduced (1) to (4) to a range of 0°C or higher and 1000°C or lower to decompose water; and heating the thermochemical hydrogen production circulating material to be oxidized (1) to (4) to a range of 800°C or higher and 1000°C or lower to spontaneously desorb oxygen.

[0026] (7) A thermochemical hydrogen production method comprising the following steps: heating water and the reduced (3) thermochemical hydrogen production circulating material to a range of above 0°C and below 1000°C to decompose water; and heating the oxidized (3) thermochemical hydrogen production circulating material to a range of above 500°C and below 1000°C to spontaneously desorb oxygen.

[0027] Invention Effects

[0028] According to one aspect of the present invention, a neutral cyclic substance capable of deoxygenating below 1000°C is provided, and a method for producing hydrogen by thermochemical decomposition using the neutral cyclic substance is provided. Attached Figure Description

[0029] Figure 1 This schematically illustrates one aspect of the invention, derived from the general formula Ca. x (RE) 1-x MO 3-δ A diagram showing the structure of perovskite oxides.

[0030] Figure 2 This is an X-ray diffraction (XRD) pattern of the products of the examples and comparative examples.

[0031] Figure 3 The graphs represent the results of oxygen desorption tests on the products of the examples and comparative examples. Figure 3 A and 3C respectively represent the information about Ca. x La 1-x FeO 3-δ and Pd / Ca x La 1-x FeO 3-δ A graph showing the TCD-based analysis results in the oxygen desorption curve. Figure 3 B and 3D respectively represent the information about Ca. x La 1-x FeO 3-δ and Pd / Ca x La 1-x FeO3-δ A graph showing the analytical results of the mass (M / e=32) in the oxygen desorption curve.

[0032] Figure 4 The graphs represent the results of oxygen desorption tests on the products of the examples and comparative examples. Figure 4 A and 4C represent the Pd / Ca ratio, respectively. x La 1-x CoO 3-δ and Pd / Ca x La 1-x MnO 3-δ A graph showing the TCD-based analysis results in the oxygen desorption curve. Figure 4 B and 4D respectively represent the Pd / Ca ratio. x La 1-x CoO 3-δ and Pd / Ca x La 1-x MnO 3-δ A graph showing the analytical results of the mass (M / e=32) in the oxygen desorption curve.

[0033] Figure 5 These are graphs showing the results of oxygen desorption tests on the products of the examples and comparative examples. Figure 5 A through 5D represent Ca respectively. x La 1-x FeO 3-δ Pd / Ca x La 1-x FeO 3-δ Pd / Ca x La 1-x CoO 3-δ and Pd / Ca x La 1-x MnO 3-δ The relationship between oxygen desorption and the Ca / (La+Ca) ratio.

[0034] Figure 6 This is a graph showing the results of an investigation into the structure near the X-ray absorption end of the X-ray absorption spectra of the embodiments and comparative examples. Detailed Implementation

[0035] Hereinafter, a preferred embodiment of the present invention will be described in detail.

[0036] In this specification, features of one aspect of the invention are described with appropriate reference to the accompanying drawings. In the drawings, the dimensions and shapes of the parts are exaggerated for clarity and are not accurately depicted. Therefore, the technical scope of one aspect of the invention is not limited to the dimensions and shapes of the parts shown in these drawings. Furthermore, one aspect of the invention is not limited to the embodiments described below and can be implemented in various ways, including modifications and alterations that can be made by those skilled in the art without departing from the spirit of one aspect of the invention.

[0037] One aspect of the present invention relates to a method comprising the general formula Ca x (RE) 1-x MO 3-δ Thermochemical hydrogen production cycle material represented by perovskite oxide.

[0038] "Thermochemical hydrogen production recycling material" refers to a substance that, in the thermochemical cycle, which is a chemical reaction that uses thermal energy to decompose water into hydrogen and oxygen to produce hydrogen and oxygen, reduces the required reaction temperature by dividing the chemical reaction into a high-temperature endothermic reaction (deoxygenation reaction) and a low-temperature exothermic reaction (water decomposition reaction). It is a substance that extracts oxygen by reacting with water and is oxidized, but then the oxygen is desorbed, reduced, and regenerated, thus returning to the original substance.

[0039] In having the general formula Ca x (RE) 1-x MO 3-δ The components of the perovskite oxides represented are Ca, RE, M, and O, as well as x, x-1, and 3-δ, as shown below.

[0040] Ca represents calcium. Calcium has a divalent oxidation state. O represents oxygen.

[0041] The rare earth element (RE) is not limited to any rare earth metal. Examples of REs include scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). There can be one or more of these. In one aspect of the invention, when there are two or more REs, the content ratio of these rare earth metals is not limited to the total RE content, as long as it satisfies the molar ratio of Ca to RE when M is set to 1 (described later). In one aspect of the invention, the RE is lanthanum. The valence of RE is typically trivalent.

[0042] M is selected from one or more metals chosen from the group consisting of Co (cobalt), Mn (manganese), and Fe (iron). In one embodiment of the invention, when there are two or more metals, the content ratio of these metals is not limited as long as the total content of M is equal to the molar ratio of Ca and RE when M is set to 1 (described later). In one embodiment of the invention, M is cobalt. In one embodiment of the invention, M is manganese. In one embodiment of the invention, M is iron. The valence of M is generally a valence higher than trivalent.

[0043] x, 1-x, and 3-δ are the molar ratios of Ca, RE, and O when M is set to 1, respectively. x is a real number in the range of 0 to 1, and in one embodiment, it is a real number in the range of 0.2 to 1. When M consists only of iron, x is not 1. In one aspect of the invention, when M is cobalt, x is a real number in the range of 0 to 1, and in one embodiment, it is a real number in the range of 0.2 to 1. In one aspect of the invention, when M is manganese, x is a real number in the range of 0 to 1, and in one embodiment, it is a real number in the range of 0.2 to 1. In one aspect of the invention, when M is iron, x is a real number in the range of greater than 0 and less than 1, and in one embodiment, it is a real number in the range of 0.2 to 0.8. 3-δ is a number that can make the overall valence of the oxide zero depending on the amount and valence of Ca, RE, and M. In one aspect of the invention, δ is a real number in the range of 0 to 1, and in one embodiment, it is a real number in the range of 0 to 0.5.

[0044] "Perovskite oxides" refer to oxides that have a perovskite crystal structure. The presence of a perovskite crystal structure in oxides can be confirmed, for example, by X-ray diffraction.

[0045] In one aspect of the invention, the oxide having the composition represented by the general formula has the composition as described above, thereby enabling it to adopt a perovskite-type crystal structure and thus function as a neutral cyclic material capable of deoxygenating at low temperatures, i.e., below 1000°C.

[0046] In one aspect of the present invention, the crystal structure of the perovskite oxide can be determined by X-ray diffraction (XRD) analysis.

[0047] Furthermore, the peak positions of the XRD spectra of perovskite-type crystal structures can be altered depending on the composition of the perovskite oxide. This is a well-known fact in the art.

[0048] Figure 1 The diagram schematically illustrates one aspect of the invention using the general formula Ca. x (RE) 1-x MO 3-δ The structure of the perovskite oxide is shown. Based on... Figure 1 M primarily forms MO6 octahedra coordinated with 6 oxygen atoms, and these structures are filled with Ca or RE in the gaps of the three-dimensional network sharing vertices. Simultaneously, there are also some structures with oxygen-deficient MO4 tetrahedral sites.

[0049] The circulating material for thermochemical hydrogen production according to one aspect of the present invention may further include a catalytic metal. The catalytic metal may be supported on the perovskite oxide described above. The supporting method can utilize conventional supporting methods such as adsorption supporting methods and water-absorbing supporting methods. Noble metals can be used as catalytic metals. The noble metal is not limited and includes platinum group metals. Examples of platinum group metals include ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt). In one embodiment, the noble metal is one or more selected from the group consisting of Rh, Pt, and Pd. In one embodiment, the noble metal is Pd. The loading amount of the noble metal is not limited, and is typically 0.01% to 5% by weight relative to the total weight of the perovskite oxide; in one embodiment, it is 0.5% to 2% by weight.

[0050] In one aspect of the invention, the circulating substance for thermochemical hydrogen production is Ca. 0.2 La 0.8 FeO 3-δ Ca 0.4 La 0.6 FeO 3-δ Ca 0.5 La 0.5 FeO 3-δ Ca 0.6 La 0.4 FeO 3-δ Ca 0.8 La 0.2 FeO 3-δ Pd / Ca 0.2 La 0.8 FeO 3-δ Pd / Ca 0.4 La 0.6 FeO 3-δ Pd / Ca 0.5 La 0.5 FeO 3-δ Pd / Ca 0.6 La 0.4 FeO 3-δ Pd / Ca 0.8 La 0.2 FeO 3-δ Pd / Ca 0.2 La 0.8 CoO 3-δ Pd / Ca 0.4 La 0.6 CoO3-δ Pd / Ca 0.5 La 0.5 CoO 3-δ Pd / Ca 0.6 La 0.4 CoO 3-δ Pd / Ca 0.2 La 0.8 MnO 3-δ Ca 0.4 La 0.6 MnO 3-δ Ca 0.5 La 0.5 MnO 3-δ Ca 0.6 La 0.4 MnO 3-δ Pd / Ca 0.8 La 0.2 MnO 3-δ Pd / CaMnO 3-δ .

[0051] The circulating material for thermochemical hydrogen production according to one aspect of the present invention, through the chemical properties of the trivalent or higher-valence transition metal (M) ions generated in the perovskite oxide, can undergo a spontaneous oxygen desorption reaction at low temperatures, particularly below 1000°C, thus enabling hydrogen production via thermochemical water splitting at temperatures below 1000°C. For example, when the circulating material for thermochemical hydrogen production according to one aspect of the present invention comprises the perovskite oxide where M is iron, the circulating material can desorb oxygen at relatively low temperatures in the range of 400°C to 1000°C, thus enabling hydrogen production within this temperature range. For example, when the circulating material for thermochemical hydrogen production according to one aspect of the present invention comprises the perovskite oxide where M is cobalt or manganese, the circulating material can desorb oxygen in the range of 800°C to 1000°C, thus enabling hydrogen production within this temperature range.

[0052] In one aspect of the invention, the perovskite oxide can be manufactured using conventional methods in the art, such as solid-phase methods, liquid-phase methods, alkoxide methods, etc. For example, it can be manufactured by mixing an aqueous solution containing a calcium compound, a rare earth metal compound, and one or more compounds selected from the group consisting of cobalt, manganese, and iron (hereinafter also referred to as the raw material compound) with an aqueous solution of a complexing agent, drying to precipitate a product containing Ca, RE, and M, and then calcining. The raw material compound can also be used as a non-aqueous solvent, such as a solution of an alcohol or an organic carboxylic acid ester.

[0053] As calcium compounds, for example, nitrates such as calcium nitrate, sulfates such as calcium sulfate, halides such as calcium chloride, and water-soluble or alcohol-soluble compounds such as alkoxides can be used.

[0054] As rare earth metal compounds, for example, they can be water-soluble or alcohol-soluble compounds such as nitrates, sulfates, halides, and alkoxides.

[0055] As a compound containing one or more of the group consisting of cobalt, manganese and iron, for example, a water-soluble or alcohol-soluble compound such as a nitrate, sulfate, halide, or alkoxide.

[0056] The complexing agent is not particularly limited, and examples include polycarboxylic acids, amino acids, and higher alcohols. Examples of polycarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, citric acid, and tartaric acid. In one embodiment, the complexing agent is citric acid. Examples of amino acids include glycine, alanine, asparagine, and aspartic acid. Furthermore, examples of higher alcohols include ethylene glycol, propylene glycol, diethylene glycol, and glycerol.

[0057] The polymerization and gelation of a mixture of aqueous solutions of the raw material compound and the complexing agent can typically be carried out at 50°C to 200°C for 1 hour to 48 hours. Furthermore, the obtained product containing Ca, RE, and M can typically be pre-calcined in atmosphere at 200°C to 500°C, for example, at 350°C for 2 hours to 6 hours, for example, 3 hours.

[0058] The calcination of the product containing Ca, RE, and M can be carried out by heating in the atmosphere at a temperature of 600°C to 1500°C for 2 to 48 hours. This yields an oxide with a perovskite-type crystal structure.

[0059] Example

[0060] Hereinafter, several embodiments related to one aspect of the present invention will be described, but it is not intended to limit the present invention to the manner shown in these embodiments.

[0061] 1. Preparation of composite oxides

[0062] The composite oxides of the examples and comparative examples were synthesized by a complex precipitation method. Citric acid and ethylene glycol, in amounts equal to 4.55 equivalents of each metal salt and their total amount, were dissolved in methanol. A gel was prepared by heating and stirring, and oxide powders were synthesized by pre-calcination and calcination. Palladium was loaded into the obtained powder at 1% by weight. The specific adjustment method is as follows.

[0063] Example 1: Ca 0.2 La 0.8 FeO 3-δ

[0064] Citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Then, Fe(NO3)3·9H2O (88 mmol), Ca(NO3)2·4H2O (18 mmol), and La(NO3)3·9H2O (70 mmol) were added, followed by ethylene glycol (800 mmol), and the mixture was stirred at room temperature for 30 minutes. After stirring, the mixture was cured at approximately 100 °C for 3 hours to prepare a gel, and then pre-calcined at 350 °C for approximately 3 hours to obtain Ca... 0.2 La 0.8 FeO 3-δ The precursor was synthesized by formally calcining the precursor powder at 1250 °C for 5 hours.

[0065] Example 2: Ca 0.4 La 0.6 FeO 3-δ

[0066] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Fe(NO3)3·9H2O (88 mmol), Ca(NO3)2·4H2O (35 mmol), and La(NO3)3·9H2O (53 mmol) were then added, followed by the addition of ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0067] Example 3: Ca 0.5 La 0.5 FeO 3-δ

[0068] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Fe(NO3)3·9H2O (88 mmol), Ca(NO3)2·4H2O (44 mmol), and La(NO3)3·9H2O (44 mmol) were then added, followed by the addition of ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0069] Example 4: Ca 0.6 La 0.4 FeO 3-δ

[0070] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Fe(NO3)3·9H2O (88 mmol), Ca(NO3)2·4H2O (53 mmol), and La(NO3)3·9H2O (35 mmol) were then added, followed by the addition of ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0071] Example 5: Ca 0.8 La 0.2 FeO 3-δ

[0072] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Fe(NO3)3·9H2O (88 mmol), Ca(NO3)2·4H2O (70 mmol), and La(NO3)3·9H2O (18 mmol) were then added, followed by the addition of ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0073] Example 6: Pd / Ca 0.2 La 0.8 FeO 3-δ

[0074] Acetone was added to a beaker, and palladium acetate was dissolved in it. Ca was then added to the beaker. 0.2 La 0.8 FeO 3-δ (Example 1) Subsequently, the solvent was removed by heating, stirring, and distillation. After drying at 120°C overnight, the obtained solid was pulverized in a mortar and calcined at 500°C for 2 hours, thereby completing the synthesis. The palladium loading relative to Ca... 0.2 La 0.8 FeO 3-δ Set to 1 weight.

[0075] Example 7: Pd / Ca 0.4 La 0.6 FeO 3-δ

[0076] Acetone was added to a beaker, and palladium acetate was dissolved in it. Ca was then added to the beaker. 0.4 La 0.6 FeO 3-δ (Example 2) Subsequently, the solvent was removed by heating, stirring, and distillation. After drying at 120°C overnight, the obtained solid was pulverized in a mortar and calcined at 500°C for 2 hours, thereby completing the synthesis. The palladium loading relative to Ca... 0.4 La 0.6 FeO3-δ Set to 1 weight.

[0077] Example 8: Pd / Ca 0.5 La 0.5 FeO 3-δ

[0078] Acetone was added to a beaker, and palladium acetate was dissolved in it. Ca was then added to the beaker. 0.5 La 0.5 FeO 3-δ (Example 3) Subsequently, the solvent was removed by heating, stirring, and distillation. After drying overnight at 120°C, the obtained solid was pulverized in a mortar and calcined at 500°C for 2 hours, thereby completing the synthesis. The palladium loading relative to Ca... 0.5 La 0.5 FeO 3-δ Set to 1 weight.

[0079] Example 9: Pd / Ca 0.6 La 0.4 FeO 3-δ

[0080] Acetone was added to a beaker, and palladium acetate was dissolved in it. Ca was then added to the beaker. 0.6 La 0.4 FeO 3-δ (Example 4) Subsequently, the solvent was removed by heating, stirring, and distillation. After drying at 120°C overnight, the obtained solid was pulverized in a mortar and calcined at 500°C for 2 hours, thereby completing the synthesis. The palladium loading relative to Ca... 0.6 La 0.4 FeO 3-δ Set to 1 weight.

[0081] Example 10: Pd / CaMnO 3-δ

[0082] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Mn(NO3)2·6H2O (88 mmol) and Ca(NO3)2·4H2O (78 mmol) were then added, followed by ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0083] Next, in Example 6, the composite oxide of Example 1 was replaced with the composite oxide prepared therein, except that palladium was loaded onto the composite oxide in the same manner as in Example 6, so that the palladium loading amount was 1 wt%.

[0084] Example 11: Pd / Ca 0.2 La0.8 CoO 3-δ

[0085] Citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Then, Co(NO3)2·6H2O (88 mmol), Ca(NO3)2·4H2O (18 mmol), and La(NO3)3·9H2O (70 mmol) were added, followed by ethylene glycol (800 mmol), and the mixture was stirred at room temperature for 30 minutes. After stirring, the mixture was cured at approximately 100 °C for 3 hours to prepare a gel, and then pre-calcined at 350 °C for approximately 3 hours to obtain Ca2+. 0.2 La 0.8 FeO 3-δ The precursor was subjected to formal calcination at 1250°C for 5 hours.

[0086] Next, in Example 6, the composite oxide of Example 1 was replaced with the composite oxide prepared therein, except that palladium was loaded onto the composite oxide in the same manner as in Example 6, so that the palladium loading amount was 1 wt%.

[0087] Example 12: Pd / Ca 0.4 La 0.6 CoO 3-δ

[0088] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Co(NO3)2·6H2O (88 mmol), Ca(NO3)2·4H2O (35 mmol), and La(NO3)3·9H2O (53 mmol) were then added, followed by the addition of ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0089] Next, in Example 6, the composite oxide of Example 1 was replaced with the composite oxide prepared therein, except that palladium was loaded onto the composite oxide in the same manner as in Example 6, so that the palladium loading amount was 1 wt%.

[0090] Example 13: Pd / Ca 0.5 La 0.5 CoO 3-δ

[0091] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Co(NO3)2·6H2O (88 mmol), Ca(NO3)2·4H2O (44 mmol), and La(NO3)3·9H2O (44 mmol) were then added, followed by the addition of ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0092] Next, in Example 6, the composite oxide of Example 1 was replaced with the composite oxide prepared therein, except that palladium was loaded onto the composite oxide in the same manner as in Example 6, so that the palladium loading amount was 1 wt%.

[0093] Example 14: Pd / Ca 0.6 La 0.4 CoO 3-δ

[0094] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Co(NO3)2·6H2O (88 mmol), Ca(NO3)2·4H2O (53 mmol), and La(NO3)3·9H2O (35 mmol) were then added, followed by the addition of ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0095] Next, in Example 6, the composite oxide of Example 1 was replaced with the composite oxide prepared therein, except that palladium was loaded onto the composite oxide in the same manner as in Example 6, so that the palladium loading amount was 1 wt%.

[0096] Example 15: Pd / Ca 0.2 La 0.8 MnO 3-δ

[0097] Citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Then, Mn(NO3)2·6H2O (88 mmol), Ca(NO3)2·4H2O (18 mmol), and La(NO3)3·9H2O (70 mmol) were added, followed by ethylene glycol (800 mmol), and the mixture was stirred at room temperature for 30 minutes. After stirring, the mixture was cured at approximately 100 °C for 3 hours to prepare a gel, and then pre-calcined at 350 °C for approximately 3 hours to obtain Ca2+. 0.2 La 0.8 FeO 3-δ The precursor was subjected to formal calcination at 1250°C for 5 hours.

[0098] Next, in Example 6, the composite oxide of Example 1 was replaced with the composite oxide prepared therein, except that palladium was loaded onto the composite oxide in the same manner as in Example 6, so that the palladium loading amount was 1 wt%.

[0099] Example 16: Pd / Ca 0.4 La 0.6 MnO 3-δ

[0100] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Mn(NO3)2·6H2O (88 mmol), Ca(NO3)2·4H2O (35 mmol), and La(NO3)3·9H2O (53 mmol) were then added, followed by ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0101] Next, in Example 6, the composite oxide of Example 1 was replaced with the composite oxide prepared therein, except that palladium was loaded onto the composite oxide in the same manner as in Example 6, so that the palladium loading amount was 1 wt%.

[0102] Example 17: Pd / Ca 0.5 La 0.5 MnO 3-δ

[0103] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Mn(NO3)2·6H2O (88 mmol), Ca(NO3)2·4H2O (44 mmol), and La(NO3)3·9H2O (44 mmol) were then added, followed by ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0104] Next, in Example 6, the composite oxide of Example 1 was replaced with the composite oxide prepared therein, except that palladium was loaded onto the composite oxide in the same manner as in Example 6, so that the palladium loading amount was 1 wt%.

[0105] Example 18: Pd / Ca 0.6 La 0.4 MnO 3-δ

[0106] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Mn(NO3)2·6H2O (88 mmol), Ca(NO3)2·4H2O (53 mmol), and La(NO3)3·9H2O (35 mmol) were then added, followed by ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0107] Next, in Example 6, the composite oxide of Example 1 was replaced with the composite oxide prepared therein, except that palladium was loaded onto the composite oxide in the same manner as in Example 6, so that the palladium loading amount was 1 wt%.

[0108] Example 19: Pd / Ca 0.8 La 0.2 MnO 3-δ

[0109] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Mn(NO3)2·6H2O (88 mmol), Ca(NO3)2·4H2O (70 mmol), and La(NO3)3·9H2O (18 mmol) were then added, followed by ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0110] Next, in Example 6, the composite oxide of Example 1 was replaced with the composite oxide prepared therein, except that palladium was loaded onto the composite oxide in the same manner as in Example 6, so that the palladium loading amount was 1 wt%.

[0111] Comparative Example 1: LaFeO 3-δ

[0112] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Fe(NO3)3·9H2O (88 mmol) and La(NO3)3·9H2O (88 mmol) were then added, followed by ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0113] Comparative Example 2: CaFeO 2.5

[0114] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Fe(NO3)3·9H2O (88 mmol) and Ca(NO3)2·4H2O (88 mmol) were then added, followed by ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0115] Comparative Example 3: Pd / LaFeO 3-δ

[0116] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Fe(NO3)3·9H2O (88 mmol) and La(NO3)3·9H2O (88 mmol) were then added, followed by ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0117] Next, in Example 6, the composite oxide of Example 1 was replaced with the composite oxide prepared therein, except that palladium was loaded onto the composite oxide in the same manner as in Example 6, so that the palladium loading amount was 1 wt%.

[0118] Comparative Example 4: Pd / CaFeO 2.5

[0119] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Fe(NO3)3·9H2O (88 mmol) and Ca(NO3)2·4H2O (88 mmol) were then added, followed by ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0120] Next, in Example 6, the composite oxide of Example 1 was replaced with the composite oxide prepared therein, except that palladium was loaded onto the composite oxide in the same manner as in Example 6, so that the palladium loading amount was 1 wt%.

[0121] Comparative Example 5: Pd / LaCoO 3-δ

[0122] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Co(NO3)2·6H2O (88 mmol) and La(NO3)3·9H2O (88 mmol) were then added, followed by ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0123] Next, in Example 6, the composite oxide of Example 1 was replaced with the composite oxide prepared therein, except that palladium was loaded onto the composite oxide in the same manner as in Example 6, so that the palladium loading amount was 1 wt%.

[0124] Comparative Example 6: Pd / LaMnO 3-δ

[0125] In Example 1, citric acid (800 mmol) was added to a beaker and dissolved in methanol (180 mL). Mn(NO3)2·6H2O (88 mmol) and Ca(NO3)2·4H2O (88 mmol) were then added, followed by ethylene glycol (800 mmol). Otherwise, the composite oxide was synthesized using the same method as in Example 1.

[0126] Next, in Example 6, the composite oxide of Example 1 was replaced with the composite oxide prepared therein. Otherwise, the composite oxide was loaded with palladium in the same manner as in Example 6 so that the palladium loading was 1% by weight.

[0127] Comparative Example 7: Pd / Ce 0.7 Zr 0.3 O2

[0128] Distilled water was added to a beaker, and palladium nitrate was dissolved. Commercially available Ceria-Zirconia (CeO₂ / ZrO₂ = 67 / 33) was added, and the solvent was removed by heating, stirring, and distillation. After drying at 120°C overnight, the resulting solid was pulverized in a mortar and calcined at 500°C for 2 hours, thus completing the synthesis. The palladium loading was set to 1% by weight relative to the cerium oxide-zirconia powder.

[0129] Comparative Example 8: Pd / Ce 0.3 Zr 0.7 O2

[0130] Distilled water was added to a beaker, and palladium nitrate was dissolved. Commercially available Ceria-Zirconia (CeO₂ / ZrO₂ = 33 / 67) was added, and the solvent was removed by heating, stirring, and distillation. After drying at 120°C overnight, the resulting solid was pulverized in a mortar and calcined at 500°C for 2 hours, thus completing the synthesis. The palladium loading was set to 1% by weight relative to the cerium oxide-zirconia powder.

[0131] Comparative Example 9: Pd / Ca 0.8 La 0.2 FeO 3-δ

[0132] Acetone was added to a beaker, and palladium acetate was dissolved in it. Ca was then added to the beaker. 0.8 La 0.2 FeO 3-δ (Example 5) Subsequently, the solvent was removed by heating, stirring, and distillation. After drying overnight at 120°C, the obtained solid was pulverized in a mortar and calcined at 500°C for 2 hours, thereby completing the synthesis. The palladium loading relative to Ca... 0.8 La 0.2 FeO 3-δ Set to 1 weight.

[0133] 2. XRD Analysis

[0134] The composite oxides prepared in the examples and comparative examples were subjected to powder X-ray diffraction (XRD) (SmartLab manufactured by Rigaku Corporation). The XRD source was set to CuKa (l = 1.5418 nm), and the range from 10 deg to 90 deg was measured in steps of 0.02 deg / 0.12 sec.

[0135] 3. Oxygen desorption test

[0136] Oxygen-temperature desorption (O2-TPD) was performed on the composite oxides prepared in the examples and comparative examples. O2-TPD was performed using Belcat A manufactured by MicrotracBEL Corp. Approximately 200 mg of sample powder was accurately weighed and introduced into a sample tube. The sample was heated to 500 °C while allowing a flow of 20% O2 / He at 30 mL / min. After a 10-minute pretreatment, the sample was cooled. After replacement with He gas, the sample was heated at 10 °C / min while allowing He to flow at 30 mL / min. The amount of O2 consumed and desorbed was analyzed. Analysis was performed using a TCD and mass spectrometer.

[0137] 4. XAFS Analysis

[0138] X-ray absorption fine structure (XAFS) measurements were performed on the composite oxides prepared in the examples and comparative examples. XAFS was conducted at the BL12C experimental station of the PhotonFactory, a high-energy accelerator research institution. The FeK (7112 eV) absorption end was analyzed using a Si(111)2 crystal spectrometer. The X-rays were detected in an ionization chamber by transmission method.

[0139] 5. Thermochemical decomposition test of water

[0140] Thermochemical decomposition tests of water were conducted on the composite oxides prepared in the examples and comparative examples. The sample powder prepared therein was subjected to a pressure of 2t and granulated into particles of 1.0 mm to 1.7 mm in a fixed-bed flow-through reactor. The sample was then subjected to a reduction pretreatment at 500°C for 10 minutes while 1% CO / N2 gas was passed through at 10 L / min. Following this, after passing through 1% H2O / N2 for 40 minutes, the amount of CO2 generated when 1% CO / N2 gas was passed through again was equivalent to the amount of oxygen removed from water by the reduced sample; therefore, the amount of CO2 generated was quantified. The amount of CO2 generated was investigated using an FT-IR analyzer (BEST Measurement Instruments SESAM-HL).

[0141] 6. Test Results

[0142] Figure 2 Figure A shows the XRD patterns of the prepared samples (Examples 6-9, Comparative Examples 3, 4, and 9). Figure 2 The image on the right is enlarged. Figure 2 The graph in A shows 2θ ranging from 31° to 34°. (Pd / LaFeO) 3-δ (Comparative Example 1), Pd / Ca 0.2 La 0.8 FeO 3-δ (Example 6) Pd / Ca 0.4 La 0.6 FeO 3-δ (Example 7), Pd / Ca 0.5 La 0.5 FeO 3-δ (Example 8), Pd / Ca 0.6 La 0.4 FeO 3-δ The diffraction lines of (Example 9) are consistent with the pattern of tilted perovskite-type LaFeO3. With the increase of Ca ratio x, the high angular shift of the strongest line is confirmed. Figure 2 Figure A (right) shows that Ca ions with small ionic radii are introduced into La sites. On the other hand, the Ca ratio is greater than 0.8 for Pd / Ca. 0.8 La 0.2 FeO 3-δ (Comparative Example 9) and Pd / CaFeO 2.5 (Comparative Example 4) The pattern is consistent with that of orthorhombic goethite-type Ca2Fe2O5, confirming that it has the same structure. Furthermore, regarding Examples 1-5 and Comparative Examples 1 and 2, which are unloaded noble metal materials, it was confirmed that the same diffraction lines as Examples 6-9 and Comparative Examples 3, 4 and 9 were detected, forming the same structure.

[0143] Figure 2Figure B shows the XRD patterns of Ca-La-Co compounds 11-14 and Comparative Example 5 containing palladium. All patterns are consistent with those of perovskite oxides, confirming the formation of the same structure.

[0144] exist Figure 2 C shows the XRD patterns of Ca-La-Mn compounds 10 and 15-19 containing palladium, and Comparative Example 6. All patterns are consistent with those of perovskite oxides, confirming the formation of the same structure.

[0145] exist Figure 3 A, 3B, and 5A, as well as Table 1, show information regarding the Ca-La-Fe system (Ca... x La 1-x FeO 3-δ The results of oxygen desorption tests of Examples 1 to 5 and Comparative Examples 1 and 2. Figure 3 A represents the TCD-based analysis results in the oxygen temperature-induced desorption curve. Figure 3 B represents the analytical result of the mass (M / e=32) in the oxygen heating desorption curve. Figure 5 A represents the relationship between oxygen desorption and the Ca / (La+Ca) ratio. According to... Figure 3 For A and 3B, the same curves were obtained by TCD and mass spectrometry. In the compositions with coexisting Ca and La (Examples 1-5), oxygen desorption was detected at temperatures below 1000°C. Furthermore, in the Ca ratio x=0.5 (Example 3), oxygen desorption was observed from approximately 400°C, with the highest desorption amount. Figure 5 Table A and Table 1 quantify the oxygen desorption amount below 1000°C, confirming that the oxygen desorption amount relative to the Ca ratio x forms a mountain-shaped sequence with x=0.5 (Example 3) as the apex.

[0146] exist Figure 3 C, 3D, and 5B, as well as Table 1, show information regarding the Palladium-supported Ca-La-Fe system (Pd / Ca). x La 1- x FeO 3-δ The results of oxygen desorption tests of Examples 6-9 and Comparative Examples 3, 4 and 9. Figure 3 C represents the TCD-based analysis result in the oxygen temperature-induced desorption curve. Figure 3 D represents the analytical result of the mass (M / e=32) in the oxygen heating desorption curve. Figure 5 B represents the relationship between oxygen desorption and the Ca / (La+Ca) ratio. From Figure 3 As can be seen from C and 3D, the results are similar to those of unloaded materials ( Figure 3Similarly, in combinations A and 3B, TCD and mass spectrometry yielded the same curves. In compositions where Ca and La coexisted (Examples 6-9 and Comparative Example 9), oxygen desorption was detected at temperatures below 1000°C. Furthermore, in a Ca ratio x = 0.5 (Example 8), oxygen desorption was confirmed from approximately 400°C, with the highest desorption amount. Figure 5 B and Table 1 quantify the oxygen desorption amount below 1000°C, confirming that the oxygen desorption amount relative to the Ca ratio x forms a mountain-shaped sequence with x=0.5 (Example 8) as the apex.

[0147] exist Figure 4 A, 4B, and 5C, as well as Table 1, show information regarding palladium-supported Ca-La-Co systems (Pd / Ca). x La 1- x CoO 3-δ The results of oxygen desorption tests in Examples 11-14 and Comparative Example 5. Figure 4 A represents the TCD-based analysis results in the oxygen temperature-induced desorption curve. Figure 4 B represents the analytical result of the mass (M / e=32) in the oxygen heating desorption curve. Figure 5 C represents the relationship between oxygen desorption and the Ca / (La+Ca) ratio. According to... Figure 4 A and 4B, TCD and mass spectrometry all obtained the same curves, and spontaneous oxygen desorption was observed in the composition where Ca and La coexist and in the temperature region below 1000 °C. Based on Figure 5 Table C and Table 1 show the quantitative results of oxygen desorption below 1000℃, indicating that oxygen desorption increases with the increase of the Ca ratio x. The divalent cation, Ca ion, occupies the A site while the Co ion, which occupies the B site, has a higher atomic valence than the trivalent cation, which contributes to the increase in desorption.

[0148] exist Figure 4 C, 4D, and 5D, as well as those shown in Table 1, relate to the palladium-supported Ca-La-Mn system (Pd / Ca). x La 1- x MnO 3-δ The results of oxygen desorption tests of Examples 10 and 15-19 and Comparative Example 6. Figure 4 C represents the TCD-based analysis result in the oxygen temperature-induced desorption curve. Figure 4 D represents the analytical result of the mass (M / e=32) in the oxygen heating desorption curve. Figure 5 D represents the relationship between oxygen desorption and the Ca / (La+Ca) ratio. According to... Figure 4 C and 4D, TCD and mass spectrometry all obtained the same curves, and spontaneous oxygen desorption was observed in the composition where Ca and La coexist and in the temperature region below 1000 °C. Based on Figure 5 Table D and Table 1 show the quantitative results of oxygen desorption below 1000℃. The oxygen desorption increases with the increase of Ca ratio x. The divalent cation, Ca ion, occupies the A site while the Mn ion, which occupies the B site, has a higher atomic valence than the trivalent cation, which contributes to the increase of the desorption amount.

[0149] Table 1 shows the results of oxygen desorption tests for Comparative Examples 7 and 8, which are samples with palladium loaded on cerium oxides. According to Table 1, as described in the literature (e.g., non-patent literature [Xiaofei et al., INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 2022, 47, 33619-33642]), no spontaneous oxygen desorption below 1000°C was observed from cerium oxides.

[0150] [Table 1]

[0151]

[0152] Figure 6 Figure A shows the results of investigating the structure near the X-ray absorption end of X-ray absorption spectrometry in Examples 6-9 and Comparative Examples 3, 4 and 9. According to... Figure 6 A, Pd / LaFeO 3-δ (Comparative Example 3) and Pd / CaFeO 2.5 The Fe K- absorption edge energy of Comparative Example 4 is the same as that of Fe2O3, therefore the iron ions contained in both are equivalent to trivalent iron. On the other hand, the Fe K- absorption edge energy of Examples 6-9 and Comparative Example 9 is located on the higher energy side compared to Fe2O3, at a Ca ratio of x=0.5 for Pd / Ca. 0.5 La 0.5 FeO 3-δ (Example 8) shows the largest displacement width. This indicates that iron ions become more than trivalent due to the coexistence of Ca and La as A sites, and iron ions reach their highest atomic valence when the Ca ratio x = 0.5. Typically, the oxidation number of Fe in iron compounds is 3 or 2, with 3 being the most stable oxidation number. On the other hand, Sr3Fe2O is known to have been found in non-patent literature [Beppu, K., Hosokawa, S., Teramura, K., Tanaka, T., Journal of Materials Chemistry A, 2015, 3, 13540]. 7-δ The Fe in this substance has an oxidation state higher than 3, and this anomalous valence state of Fe exhibits a unique deoxidizing ability to eliminate its valence instability. It is believed that Ca... x La 1-x FeO 3-δThe Fe in it also has an oxidation number higher than 3, which is related to the excellent oxygen desorption properties.

[0153] To investigate the composition ratio of iron ion species contained in Examples 6-9 and Comparative Examples 3, 4, and 9, self-modeling curve resolution (SMCR, referencing non-patent literature [Lawton, WHand Sylvestre, EA Techno metrics 1971, 13, 617]) was used. Figure 6 The structural spectrum near the X-ray absorption end of A was separated by X-ray absorption spectroscopy. Figure 6 B shows the separated component spectra. From Figure 6 As can be seen from B, components 1, 2, and 3 faithfully reproduce the... Figure 6 Pd / LaFeO shown in C 3-δ (Comparative Example 3) Pd / CaFeO 2.5 (Comparative Example 4) and Pd / Ca 0.5 La 0.5 FeO 3-δ The measured spectrum of (Example 8). This indicates that the Fe in a series of samples with different Ca / La ratios (Examples 6-9 and Comparative Examples 3, 4 and 9) is composed of the iron content of these three samples.

[0154] exist Figure 6 In D, the dependence of the ratios of components 1, 2, and 3 on the Ca / La ratio was determined. From Figure 6 In D, the amount of Fe in component 3 was confirmed to be... Figure 5 The oxygen adsorption sequence of B is consistent, and the oxygen adsorption of a series of samples with different Ca / L ratios strongly indicates that component 3, namely Ca and La, is dominated by Fe in the phase occupying an equal amount of A sites.

[0155] Regarding the Pd / Ca ratio observed to contain significant oxygen desorption below 1000℃ 0.5 La 0.5 FeO 3-δ (Example 8), Pd / Ca 0.5 La 0.5 CoO 3-δ (Example 13) Pd / CaMnO 3-δ(Example 10) A water splitting experiment was conducted. After sample particles were placed in a fixed-bed flow-through reactor, a reduction pretreatment was performed by circulating 1% CO / N2 gas at 500°C to desorb oxygen equivalent to the oxygen desorption amount at 1000°C. Then, after circulating 1% H2O / N2 for 40 minutes, the amount of CO2 generated when circulating 1% CO / N2 gas again was equivalent to the amount of oxygen removed from water by the reduced sample; therefore, the amount of CO2 generated was quantified. The results are shown in Table 2.

[0156] [Table 2]

[0157]

[0158] According to Table 2, excellent hydrolysis ability was confirmed in any sample, and spontaneous desorption and hydrolysis reactions were confirmed to occur cyclically below 1000°C.

Claims

1. A circulating substance for thermochemical hydrogen production, characterized in that, Contains the general formula Ca x (RE) 1-x MO 3-δ The perovskite-type oxide represented, In the formula, RE is one or more selected from the group composed of rare earth metals, M is one or more selected from the group composed of cobalt, manganese and iron, x is a real number in the range of more than 0 and less than 1, and δ is a real number in the range of more than 0 and less than 1. When M is composed of only iron, x is not equal to 1.

2. A circulating substance for thermochemical hydrogen production, characterized in that, Contains the general formula Ca x (RE) 1-x MO 3-δ The perovskite-type oxide represented, In the formula, RE is one or more selected from the group consisting of rare earth metals, M is one or more selected from the group including cobalt and manganese, x is a real number in the range of more than 0 and less than 1, and δ is a real number in the range of more than 0 and less than 1.

3. A circulating substance for thermochemical hydrogen production, characterized in that, Contains the general formula Ca x (RE) 1-x MO 3-δ The perovskite-type oxide represented, In the formula, RE is one or more selected rare earth metals, M is iron, x is a real number in the range of 0 and less than 1, and δ is a real number in the range of 0 and less than 1.

4. Use of a circulating material for thermochemical hydrogen production according to any one of claims 1 to 3 in thermochemical hydrogen production.

5. A thermochemical method for producing hydrogen, characterized in that, Includes the following steps: Heating water and the reduced thermochemical hydrogen production circulating material according to any one of claims 1 to 3 to a range of above 0°C and below 1000°C to decompose water; and The circulating material for thermochemical hydrogen production according to any one of claims 1 to 3 is heated to a temperature range of 800°C or higher and 1000°C or lower to allow oxygen to desorb spontaneously.

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